Long Term Evolution (LTE) has emerged as a high speed and capacity radio communication standard that offers radio and core network improvements over predecessor Second and Third Generation (2G and 3G) networks such as Global System for Mobile Communications (GSM) and Universal Mobile Telecommunications System (UMTS). While such predecessor or “legacy” networks may employ a combination of circuit-switched (CS) and packet-switched (PS) networks for data transfer, LTE networks may be entirely packet-switched and accordingly may rely on an Internet Protocol (IP)-based network architecture for data transfer.
Despite the improvements offered by LTE over the various legacy networks, many currently deployed LTE networks may not be able to provide full support for voice calls (known as Voice over LTE (VoLTE)). Accordingly, while users may enjoy the high data rates of LTE for other packet data uses (such as e.g. Internet access, application data, streaming media, etc.), mobile terminals may need to rely on circuit-switched legacy networks to support voice calls. A mobile terminal may thus need to transition, or “fall back”, to a legacy circuit-switched network in order to both make and receive voice calls. Such procedures are known as Circuit-Switched Fallback (CSFB).